Infections of the skin are caused to a vast extent by skin-pathogenic bacteria or fungi. Their treatmentxe2x80x94depending on the particular pathogenxe2x80x94is carried out either using antibacterial or using antimycotic agents.
Staphylococci and streptococci are a cause of bacterial infections of the skin in about 70% of all cases. Further important pathogens of bacterial skin infections which may be mentioned are Proteus sp. Other bacteria which grow under aerobic and anaerobic conditions, such as enterococci, Escherichia coli, Pseudomonas aeruginosa and Klebsiella come into question far less frequently as pathogens of skin infections.
Yeasts, on the other hand, have recently markedly gained in importance as pathogens of skin infections, in particular in immunosuppressed patients, in which the mucocutaneous and systemic spread of the yeasts can be a therapeutic problem.
Since bacteria as a rule have no noticeable keratinase activity, which is necessary for the start of an infection, fungal infections are frequently a starting point for the emergence of bacterial secondary infections.
The present invention therefore relates to substances which are suitable for the topical treatment both of fungal infections and of bacterial infections of the skin. Topical wide-spectrum antiinfectives according to the present invention were until now not available as monopreparations for the treatment of skin infections.
In the choice of agents for antibacterial therapy, inter alia, development of resistance must in particular be taken into consideration. Especially in the case of longer treatment, the pathogen spectrum should be determined by wound smears and its behavior checked with respect to the compositions used. Furthermore, note must be made of contact sensitivities and intolerability reactions. Especially in the case of neomycin and gentamycin, which have been used for many years in the treatment of skin infections, the danger of sensitization is high.
For staphylococcal infections of the skin, which are frequent everywhere, erythromycin and clindamycin are frequently also employed in addition to gentamycin. They are used both locally, mainly in acne therapy, and also systemically.
However, owing to systemic administration, which has been carried out for many years, therapy-resistant bacterial strains have developed both against gentamycin and against erythromycin and clindamycin to a great extentxe2x80x94even against modern gyrase inhibitors, such as, for example, ofloxacin. In a retrospective study, Th. Forssmann et al. (H+G Volume 69, Part 12, 1994, pp. 828-832) analyzed the antibiotic resistance of Propionibacterium acnes and Staphylococcus epidermidis in acne patients who were pretreated with antibiotics.
The investigations show that, with respect to Propionibacteria, resistances were found to erythromycin in 36% and to clindamycin in 11% of the cases. With Staphylococcus epidermidis, resistances were found to erythromycin in 90% and to clindamycin in 40% of the cases.
The increasing number of resistances of enterococci to gentamycin (up to 50% in isolates from various centers) gives reason to think particularly the same strains also are resistant to many other substances, including vancomycin (Martindale 30th Edition, 1993, pp. 171,2).
The same problem exists with gentamycin-resistant Staphylococcus aureus strains, which as a rule are also insensitive to methicillin and ofloxacin (Martindale 30th Edition, 1993, pp. 171,2 own investigations).
It is furthermore known from the literature that among the conventional antibiotics cross-resistances are developing to an increasing extent. Thus, inter alia, in the case of patients who were only pretreated with erythromycin, in 20% of the cases a resistance to clindamycin was also observed.
For the reasons outlined, it no longer applies as a therapeutic standard today also to employ topically antibiotics which are used systemically.
In the search for a new therapeutic standard for antibiotically active substances to be used topically, it has now surprisingly been found that substances from the 1-hydroxy-2-pyridone class, which until now have found their way into therapy exclusively as antimycotics, are also excellently suited for the topical treatment of bacterial skin infections.
In more recent experiments, it was possible, in particular, to show that 1-hydroxy-2-pyridones have an uninterrupted spectrum of action against the bacterial species occurring in skin infections, in particular also against antibiotic-resistant strains. In combination with the already-known antimycotic properties of the 1-hydroxy-2-pyridones, this is an extremely important finding for the successful treatment of skin infections, as the hitherto obligatory bacterial identification with subsequent resistance testing on treatment with the substances according to the invention is no longer necessary, which in the end also leads, inter alia, to a substantial reduction in the treatment costs.
The invention therefore relates to the use of 1-hydroxy-2-pyridones of the formula I 
in which
R1, R2 and R3, which are identical or different, are a hydrogen atom or alkyl having 1-4 carbon atoms, and
R4 is a saturated hydrocarbon radical having 6 to 9 carbon atoms or a radical of the formula II 
xe2x80x83where
X is S or O,
Y is a hydrogen atom or up to 2 halogen atoms such as chlorine and/or bromine,
Z is a single bond or the divalent radicals O, S, xe2x80x94CR2 (R=H or (C1-C4)-alkyl) or other divalent radicals having 2-10 carbon and optionally O and/or S atoms linked in the form of a chain, wherexe2x80x94if the radicals contain 2 or more O and/or S atomsxe2x80x94the latter must be separated from one another by at least 2 carbon atoms and where 2 adjacent carbon atoms can also be linked to one another by a double bond and the free valencies of the carbon atoms are saturated by H and/or (C1-C4)-alkyl groups,
Ar is an aromatic ring system having up to two rings which can be substituted by up to three radicals from the group consisting of fluorine, chlorine, bromine, methoxy, (C1-C4)-alkyl, trifluoromethyl and trifluoromethoxy in free or in salt form,
for the production of a pharmaceutical for the topical treatment of skin infections which are caused by fungi and bacteria.
In the radicals xe2x80x9cZxe2x80x9d, the carbon chain members are preferably CH2 groups. If the CH2 groups are substituted by C1-C4 alkyl groups, CH3 and C2H5 are preferred substituents. Exemplary radicals xe2x80x9cZxe2x80x9d are:
xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94CH2xe2x80x94, xe2x80x94(CH2)mxe2x80x94 (m=2-10), xe2x80x94C(CH3)2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Sxe2x80x94, xe2x80x94SCH2xe2x80x94, xe2x80x94SCH(C2H5)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94CH2Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94CHxe2x95x90CHxe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94CH2CH2Oxe2x80x94, xe2x80x94SCH2CH2CH2Sxe2x80x94, xe2x80x94SCH2CH2CH2CH2Oxe2x80x94, xe2x80x94SCH2CH2OCH2CH2Oxe2x80x94, xe2x80x94SCH2CH2OCH2CH2Oxe2x80x94CH2CH2Sxe2x80x94 or xe2x80x94Sxe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94Sxe2x80x94.
The radical xe2x80x9cSxe2x80x9d denotes a sulfur atom, the radical xe2x80x9cOxe2x80x9d denotes an oxygen atom. The term xe2x80x9cArxe2x80x9d denotes phenyl or condensed systems such as naphthyl, tetrahydronaphthyl and indenyl, and also isolated systems such as those which are derived from biphenyl, diphenylalkanes, diphenyl ethers and diphenyl thioethers.
In the formula I, the hydrocarbon radical R4 is an alkyl or cyclohexyl radical which can also be bonded to the pyridone ring via a methylene or ethylene group or can contain an endomethyl group. R4 can also be an aromatic radical which, however, is preferably bonded to the pyridone radical via at least one aliphatic carbon atom.
Important representatives of the class of compound characterized by the formula I are:
6-[4-(4-chlorophenoxy)phenoxymethyl]-1-hydroxy-4-methyl-2-pyridone, 6-[4-(2,4-dichlorophenoxy)phenoxymethyl]-1-hydroxy-4-methyl-2-pyridone, 6-(biphenylyl-4-oxymethyl)-1-hydroxy-4-methyl-2-pyridone, 6-(4-benzyl-phenoxymethyl)-1-hydroxy-4-methyl-2-pyridone, 6-[4-(2,4-dichlorobenzyloxy)phenoxymethyl]-1-hydroxy-4-methyl-2-pyridone, 6-[4-(4-chlorophenoxy)phenoxymethyl]-1-hydroxy-3,4-dimethyl-2-pyridone, 6-[4-(2,4-dichlorobenzyl)phenoxymethyl]-1-hydroxy-3,4-dimethyl-2-pyridone, 6-[4-(cinnamyloxy)phenoxymethyl]-1-hydroxy-4-methyl-2-pyridone, 1-hydroxy-4-methyl-6-[4-(4-trifluoromethylphenoxy)phenoxymethyl]-2-pyridone, 1-hydroxy-4-methyl-6-cyclohexyl-2-pyridone, 1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)-2-pyridone, 1-hydroxy-4-methyl-6-n-hexyl-, -6-iso-hexyl-, -6-n-heptyl- or -6-iso-heptyl-2-pyridone, 1-hydroxy-4-methyl-6-octyl- or -6-iso-octyl-2-pyridone, in particular 1-hydroxy-4-methyl-6-cyclohexylmethyl- or -6-cyclohexylethyl-2-pyridone, where the cyclohexyl radical in each case can also carry a methyl radical, 1-hydroxy-4-methyl-6-(2-bicyclo[2,2,1]heptyl)-2-pyridone, 1-hydroxy-3,4-dimethyl-6-benzyl- or -6-dimethylbenzyl-2-pyridone or 1-hydroxy-4-methyl-6-(xcex2-phenylethyl)-2-pyridone.
The term xe2x80x9csaturatedxe2x80x9d here designates those radicals which contain no aliphatic multiple bonds, i.e. no ethylenic or acetylenic bonds. The term xe2x80x9ctopicalxe2x80x9d is understood as meaning the local action on the skin. The term xe2x80x9cfungusxe2x80x9d means all chlorophyll-free cells with cellulose or chitin in the cell walls which contain chromosomes in the cell nucleus. The fungi in particular include yeast, mold fungi, skin, hair and budding fungi. The term xe2x80x9cbacteriaxe2x80x9d means microorganisms with heterotrophic or autotrophic metabolisms, which have no chromosomal nucleus. The bacteria include gram-positive and gram-negative microorganisms, in particular those which can grow on the skin surface of humans or animals, for example skin-pathogenic bacteria of the genera staphylococci, streptococci, corynebacteria, propionibacteria and Proteus, and also other aerobic and anaerobically growing bacteria such as enterococci, Escherichia coli, Pseudomonas and Klebsiella. The term xe2x80x9cantibiotic resistancexe2x80x9d means the property of microorganisms to be insensitive to the therapeutically achievable active compound concentration of an active compound.
The abovementioned compounds of the formula I can be employed both in free form and as salts; use in free form is preferred.
If organic bases are used, poorly volatile bases are preferably employed, for example low molecular weight alkanolamines such as ethanolamine, diethanolamine, N-ethylethanolamine, N-methyldiethanolamine, triethanolamine, diethylaminoethanol, 2-amino-2-methyl-n-propanol, dimethylaminopropanol, 2-amino-2-methylpropanediol, triisopropanolamine. Further poorly volatile bases which may be mentioned are, for example, ethylenediamaine, hexamethylenediamine, morpholine, piperidine, piperazine, cyclohexylamine, tributylamine, dodecylamine, N,N-dimethyldodecylamine, stearylamine, oleylamine, benzylamine, dibenzylamine, N-ethylbenzylamine, dimethylstearylamine, N-methylmorpholine, N-methylpiperazine, 4-methylcyclohexylamine, N-hydroxyethylmorpholine. The salts of quaternary ammonium hydroxides such as trimethylbenzylammonium hydroxide, tetramethylammonium hydroxide or tetraethylammonium hydroxide can also be used, and furthermore guanidine and its derivatives, in particular its alkylation products. However, it is also possible to employ, for example, low molecular alkylamines such as methylamine, ethylamine or triethylamine as salt-forming agents. Salts with inorganic cations, for example alkali metal salts, in particular sodium, potassium or ammonium salts, alkaline earth metal salts such as in particular the magnesium or calcium salts, and salts with di- to tetravalent cations, for example the zinc, aluminum or zirconium salt, are also suitable for the compounds to be employed according to the invention.
The active compounds of the formula I to be employed in the preparations can be prepared, for example, by the process according to U.S. Pat. No. 2,540,218.
For use according to the invention of the compounds mentioned, liquid to semisolid pharmaceutical preparations are suitable, in particular solutions, cream, ointment and gel preparations, where the latter are preferably used because of their increased release of active compound. The production of these preparations is carried out in a manner known per se with addition of the active compound employed according to the invention. Of the abovementioned 1-hydroxy-2-pyridones, the preparations according to the invention can contain one compound or alternatively two or more in combination.
In the preparations according to the invention, the active compound is incorporated in amounts which are customarily between approximately 0.1 and approximately 5%, preferably between 0.5 and 1%.
Using the pharmaceuticals according to the invention, a drastic cure can be achieved in the topical treatment of infections of the skin. The compositions according to the invention can also be employed for the treatment of acne, rosaceaxe2x80x94a disease of still unclarified etiologyxe2x80x94and of erythrasma, a pseudomycosis of the skin caused by Corynebacterium minutissimum. 